"We are marching this digital music revolution around the world," said Steve Jobs, chief executive of Apple Worldwide.

Although the market is still in its infancy, more than 500,000 music tracks have been downloaded legally in the UK so far this year.

The legal market is expected to take off this year as more homes get broadband, more legal sites are launched and the record industry's legal action against "pirates" takes hold.

Mr Jobs said iTunes' biggest competitor was not Napster or OD2 but piracy.

"Piracy is the biggest market for downloads - we have to understand it and offer a better product," he said.

ITUNES US SUCCESS

85 million songs sold so far

70% market share of the online music market

Three million iPods sold

"We now have the most popular place in the world to buy online music," he added.

When asked what owners of MP3 players should do if they wanted to download music from iTunes - which is incompatible with MP3 players - Mr Jobs said: "I think they should get an iPod."

Many online services use the Windows Media Audio format, but iTunes uses a different format that means tracks downloaded for the store can be played on just one portable device - the iPod.

Fifty percent of the digital music players in the world will not work with Apple's music store.

But downloaded songs can be copied on to a CD.

Allowing people to discover new music and still support the artists is really important

Alicia Keys

Peter Jamieson, chairman of the British Phonographic Industry, said he welcomed iTunes' foray into Europe.

"It's great news for the UK music industry, but it's even better news for UK music fans," he said.

Mark Mulligan, a media analyst for Jupiter Research, said the European online music market would finally be able to compete with illegal services.

"I think we will see an initial surge in sales from iPod users but then slow, organic growth," he said.

But the Association of Independent Music (Aim) said many labels would not make their repertoire available to the new service because negotiations with Apple had broken down.

"We welcome the arrival of iTunes in the UK, but are disappointed that our members have been unable to agree terms for licensing their repertoire to the service," said Aim's chief executive Alison Wenham.

Apple said they have "signed dozens of independent labels in the UK but we want to sign more".

Singer Alicia Keys, who was the guest star at the launch event, said she supported iTunes.

Consumers are hungry to get music from new convenient and flexible sources

Jay BermanInternational Federation of the Phonographic Industries

"Allowing people to discover new music and still support the artists is really important. ITunes is revolutionary," she said, after performing four songs including a tribute to Ray Charles.

Major record labels are keen for industry-backed music stores to launch in Europe to stop pirated tracks being swapped over the internet.

Jay Berman, chief executive of the International Federation of the Phonographic Industries (IFPI) said the launch of iTunes was proof that the music industry was embracing digital music.

Not everyone has an iPod, a credit card or 99p to spend on a single download

Russell CookeWippit

"Consumers are hungry to get music from new convenient and flexible sources," he said.

"The recording industry has proved its commitment to making a huge catalogue of its music available online."

Another download service, Wippit.com, said iTunes would be a great place for music fans with credit cards to download major label music files.

"We know that not everyone has an iPod, a credit card or 99p to spend on a single download," said Wippit label manager Russell Cooke.